Corrosion inhibitor

Abstract

A corrosion inhibitor for ferrous and non-ferrous aqueous systems comprising (a) a water soluble phosphonic acid or salt thereof, preferably an amino methylene phosphonic acid; (b) a phosphonocarboxylic acid, preferably a phosphonoalkane carboxylic acid; (c) an azole, preferably benzotriazole or tolyltriazole; and (d) a water soluble molybdate salt, preferably sodium molybdate.

We claim: 
     
       1. A composition for use in inhibiting corrosion of metallic surfaces including mild steel in an alkaline cooling water system in which the active components consist essentially of (a) 0.3-30% by wt. of nitrilotrimethylene phosphonic acid or a salt thereof; (b) 0.4-40% by wt. of 2-phosphonobutane tricarboxylic acid-1,2,4; (c) 0.4-40% by wt. of tolyltriazole; and (d) 0.5-50% by wt. of an alkali metal molybdate. 
     
     
       2. A method of inhibiting the corrosion of metallic surfaces including mild steel in an alkaline cooling water system which comprises incorporating in the cooling water an effective amount of a composition according to claim 1.